There are 2 main muscle fibre types, Slow twitch (Type I) and Fast twitch
(Type II). Fast twitch fibers can then be split into 2 sub categories,
Fast-oxidative (Type IIa) and Fast-glycolytic (Type IIb). Type IIa fibres have a
greater potential for prolonged activity than type IIb fibres which tire very
rapidly but produce the greatest power, as required in sprinting, jumping and
throwing. Athletes with predominantly type I fibres are ideally suited to long
distance events, 1/2 marathon +. Athletes with predominantly type II fibres are
ideally suited to sprinting, jumping and throwing, and athletes with a mix of
both types are better suited to races between 1500 and 10,000m.

So how do you determine what composition of fibres you have? Well, there are
various methods, the most accurate, and least appealing is to have a muscle
biopsy taken and analyzed. This is a rather invasive method so you may want to
try a less accurate test that you can do yourself in the gym. It should be noted
before I continue that the composition of muscles can vary greatly between
muscle groups in a single individual.

The following test should help give an indication if there is a balance in
favour of type I or type II fibres.

For the test you will need a dumbell, barbell, or machine with small weight
increments.

During the test rest for 2 minutes between trials to rebuild your energy
stores

To keep the test uniform: lift for 2 seconds, pause, and lower for 4 seconds

Repeat part 3, increasing the weight in increments of 1-4Kg, until you
reach a maximum weight you can lift at one time. This represents your 1
repetition maximum (1RM). To avoid exhaustion, try to determine this in less
than 8 trials.